Traffic control system



Sept. 15, 1970 J. s. WAPNER 3,529,285

TRAFFIC CONTROL SYSTEM Filed May ll, 1967 i ssheetsheet 1 N 8 K9) ZONE 2Z0 fzf l mfc@ @Home l E" ZZ\` Zo/yfmrf Z4 N ZONEmrE ZONE e all /ys FH/"YQ8 fw /Vbgy -Zo-5 27 pf- 29122)- f :o4 "0 v 1oz F- 36 Q -|150 l pif-Ha@5 Qb- 105 HO 100 j HP1. a man T/M:

l y l SEM/)070mm fill?- M #L c Adm/74770 a y -1oo 10b I ,O8 Q5 /HA l MH266( s: EW mQP//YG +IA 56 5' C D Ml/7CH Q0 ya L58 I w30 l Ggf/y 50 1 -2YELLOW PED "8 3 ,P50 @Pff/y 1F50 ycuok/ 1O 150l I5Z 74 -154 'tf-F W( ,48158 A56 ^1e2 im fr 134 136 |38 MO I4?. 144 1Z0 122 IZA 126 128 '130 9 ly Gra-fw Yaas/Pw 6fm-vidad Y v INVENTOR. MANUAL 66799 6.. Me/v5? QU-94?-l-LCTL- WM 5 Sheet's'fheet 2 IIT- Josep/f 5. Mop/V69,

Arm/wey Sept. 15,.l 1970 `.1. s. WAPNR TRAFFIC CONTROL SYSTEMl Filed May1l, 1967 United States Patent Office 3,529,285 Patented Sept. 15 1970 59 vTRAFFIC CONTROL SYSTEM .Ioseph S. Wapner, Levittown, Pa., assignor toFischer &

Proctor Co., Warminster, Pa., a corporation of PennsylvaniaContinuation-impart of application Ser. No. 359,831, Apr. 15, 1964. Thisapplication May 11, 1967, Ser. No.

Int. cl. Gosg 1/08 U.S. Cl. 340-37 7 Claims ABSTRACT 0F THE DISCLOSURERELATED APPLICATION This application is a continuation-in-part of thepending application bearing the same title, Ser. No. 359,831, filed Apr.15, 1964, now abandoned.

This invention relates generally to traflic control systems, and moreparticularly to an analog computer for operating a traffic signalcontroller and adapted to maintain an optimum degree of flow efficiencyat an intersection under fluctuating vehicular traffic conditions.

The flow of traffic at an intersection of two roadways is generallygoverned by a signal controller whose operating cycle has two phaseswhich shall hereafter be disignated phase A and phase B. In phase A, ago or green signal is accorded to traffic in the first road (X) and astop or red signal is given to traffic in the second road (Y), whereasin the alternative phase B, the signals are reversed. The point of phasetransfer in the operating cycle is usually referred to as the split. Insome instances, the controller may include a warning or yellow signalwhich when a split occurs is presented for a predetermined intervalbefore the go or stop signal is given.

In either phase of operation, the signal controller necessarily imposesa delay on the flow of traffic in one of the two intersecting roads.Since the purpose of any traffic controller system is to minimize delayand thereby keep traffic moving, the basic problem one is confrontedwith in the operation of a signal controller is when to effect the phasesplit in the operating cycle. For example, if the flow of traffic onroad X is heavy while that on road Y is very light, it is obviouslydesirable to hold the signal controller in phase A and to transfer tophase B only when a vehicle appears on road Y, and to revert to phase Bas soon as this vehicle clears through the intersection. But when thetraffic intensity on both roads is heavy, then the split must bemanipulated to take this condition into account in order to promote flowefliciency. Obviously a traffic controller which alternately switchedfrom phase A to phase B periodically without regard to actual traflicconditions would militate against the efficient flow of traffic.

If on the other hand the traffic pattern at a given intersection in thecourse of a day were more or less predictable, it might be possible toprogram the operation of a singal controller to minimize delay at alltimes, so that the controller would function in one manner to take careof peak traffic in the course of the day, and would function in otherways when other predictable patterns are encountered. However, whiletraffic peaks may generally be anticipated at given intersections, theactual pattern of traffic is so variable in the course of any day that aprogrammed controller falls far short of attaining the desiredobjective.

It is for this reason that computers have been developed to measureprevailing traffic parameters and to actuate the signal controller as afunction of actual rather than estimated parameters. In trafficengineering the three main parameters which are usually measured forthis purpose are speed, density and volume, Trafiic density is ameasurement of the number of vehicles occupying a unit length of roadwayat a given moment. Traffic speed is the speed of vehicles flowing uponthe roadway, while traffic volume is the number of vehicles passing agiven point during a specified time period.

In computers of the type heretofore devised for automatic actuation of asignal controller, the computer is designed ot measure one or more ofthe parameters of density, speed and volume by means of digitaltechniques. In density measurement, the number of vehicles entering agiven space is recorded and the number departing from the same space isrecorded in order to arrive at a count representing the number withinthe space, In volume measurement, the number of vehicles passing a givenpoint per hour is counted. In speed measurement, the time it takes for avehicle to travel between two spaced points is determined.

The nature of vehicles is such that they do not lend themselves totreatment as digits. Hence computers for traffic control whose operationis digital are incapable of effecting optimum control under fluctuatingtrafiic conditions. If all vehicles were of the same size and if theytravelled at the same speed, Athey could readily be handled as digitsfor purposes of computation. But this is not actually the case and bycounting the number of vehicles passing a given point, the countattained during a prescribed interval does not reveal the true nature oftraflic. For instance, twenty trailer trucks successively passing apoint during a given interval will give a low count, whereas during thesame interval many more small cars could have passed, yet the trailertrucks constitute a much heavier traffic condition.

In view of the foregoing it is the principal object of this invention toprovide a system including a computer affording an analog of actualtraffic conditions, which analog value governs the operation of a signalcontroller to effect a split therein in a manner promoting optimum flowefficiency in a fluctuating traffic pattern.

More specifically, it is an object of the invention to provide a trafficcontrol system of the above type wherein the presence or absence ofvehicles within an elongated zone in a lane in advance of anintersection is detected to produce occupancy and non-occupancy valueswhich determine the duration of a timing interval, whereby said intervalconstitutes an analog of actual traffic flow, the signal controllerbeing caused to split at the conclusion of the interval.

A further object of the present invention is to provide in system whichis flexible in operation so that at different times or for differenttraffic problems it may operate in different modes. Using basically thesame elements, switching is provided to secure a fully automatic system,a semiautomatic system, a fixed time cycle system, or a system involvingmanual control under special circumstances when that is required. Thesystem also may be readily adjusted to secure optimum operation duringany predetermined part of a day or under special circumstances involvingunusual traflic congestion.

Briefly stated, these objects are accomplished in a system provided witha signal traffic controller positioned at an intersection, a detectorbeing disposed within a zone in a lane in advance of the intersectionwhose length is sufficient to include a plurality of vehicles, thedetector acting to sense the presence of any vehicle or a portionthereof within said zone or the absence of all vehicles therefrom toproduce a first value representing the state of zone occupancy and asecond value representing the state of zone non-occupancy, the detectorbeing coupled to a timer which runs from a start point to a finish pointat a rate which in response to said first value is slow and which inresponse to said second value is fast whereby the resultant timinginterval has a duration which is an analog of the actual trafficconditions detected in said zone, the controller being caused to splitwhen said finish point is reached to cause a change of phase delayingtraffic flow in said lane.

For a better understanding of the invention as well as further objectsthereof, reference is made to the following detailed description to beread in conjunction with the accompanying drawings, in which:

F-IG. 1 is a schematic diagram of one embodiment of the inventioninvolving a combination of electromechanical and electronic elements;

FIG. 2 is a schematic diagram of a system which is Wholly electronic andinvolves no electromagnetic elements except simple and reliable relays;

FIG. 3 shows in block diagram the essential elements of the analogsystem in generalized form; and

FIG. 4 is a graph representing the operation of the timer.

Referring first to FIG. l, there is illustrated the simplest and usualtype of intersection of two streets or roads 2 and 4 which will behereinafter respectively referred to as a north-south, NS highway and aneast-west, EW highway having the intersection 6. As will become evidentas the description proceeds, the apparatus which will be described maybe readily extended to more elaborate configurations of intersectionsmerely by increase of the steps involved in a complete cycle ofoperation. Thus the invention may be extended to the control of trafficat intersections of three or more highways, special intersectionsinvolving dead ends of one or more highways, intersections at whichcertain right turns or the like may be permitted safely either at alltimes or during certain times when cross traffic is also permitted, orthe like. The basic system may be readily modified either by adjustmentsor by extensions for these situations. For simplicity the descriptionwill be first confined to the simple intersection shown.

One of the aspects of the control system is that for each approach tothe intersection it does not merely detect vehicles at a particularpoint; rather, it detects and responds to vehicles which are presentwithin an extended length of each approach. At 8, 10, 12 and 14 thereare indicated the lengths or areas of the approaches to the intersectionwithin which vehicles are detected. These lengths or zones may be ofdifferent extents in accordance with average travelling conditions ofvehicles on the respective highways. For example, assuming that thehighway 2 carries relative high speed trafiic and the highway 4 is asecondary one on which traffic is generally slower, or should be forsafety, the zones 8 and `10 may be substantially longer than the zones12 and 14. These zones may have lengths ranging upwardly from 35 feetunder most conditions, the most suitable length being determined fromtraffic studies. The fact that the length will generally be fixed is notdetrimental to the flexibility of the system since the timing devices inthe system may be adjusted to secure good compensation for varying con;ditions.

In accordance with the invention, the basic aspect is that any vehiclewithin the zones 8, 10, 12 and `14 should be detected. The invention isnot concerned with the particular detecting means used, detectors orpickup devices of applicable type being well known. Typically, forexample, the detection areas are delimited by conductive loops energizedby high frequency currents and subjected to inductance variations due tothe metal of the vehicle. The loops for a single highway may beconnected in series or in parallel, and such connections to a responsivedevice are indicated at 16 and 18, these effectively providingrespective signals for the NS and EW highways to a device 20 which maybe called the vehicle detector. The device 20 may, for example, be of awell known type in which a high fixed frequency current is producedfeeding the loops delimiting the detection areas and in which means isprovided sensitive to phase shift giving rise to output currents whichcorrespond to the presence of vehicles in the respective areas. Theseoutputs are indicated as providing currents to the windings ofrespective zone state relays 22 and 24. The former relays `will beenergized when any vehicle or a portion thereof is within the detectionzones 8 or 10; while the relay 24 will be energized when any vehicle ora portion thereof is within the zones 12 or 14. Similar operations ofrelays individual to the intersecting highways may be produced by otherdetecting arrangements, radar, capacitive, supersonic, or the like. Manysuch devices are well known and for the purposes of the presentinvention any may be used provided it is suitable to detect the presenceof vehicles in predetermined areas. Even multiple treadle systems may beused such as will respond to the entering and leaving of the areas byVehicles.

The relay 22 is provided with a movable contact 26 normally closed witha fixed contact 30` and adapted to disengage this contact and close witha fixed contact 32 when the relay is energized. The relay 24 has acorresponding movable contact 28 and the respective normally closed andnormally open contacts 34 and 36. A further element of the system is afunction switch 38 having five contact banks l, Il, III, IV and V, andthree alternative positions, a, b and c. The movable contacts 40, 42,44, 46 and 48 of the respective banks are ganged on a common shaft. Thepositions a, b and c are indicated by the descriptive legends FixedTime, Semi-Automatic, and Automatic The significance of these terms maybe more conveniently described as follows:

Fixed Time indicates the selection of operation in a fixed time cyclewith predetermined intervals corresponding to the usual traiic signalsystem which is clock controlled. In th'e present system such operationis secured by utilization of RC arrangements.

Semi-Automatic implies an operation which, though vehicle controlled aswill be described hereafter, gives preferential treatment to onehighway, the control light for which is normally green so that highspeed trafic thereon will ordinarily be maintained except as required bythe presence of one or more vehicles on a minor cross road.

Automatic refers to a selected operation in which the type of preferencejust mentioned is not given, though some preference for the mostdesirable maintenance of traffic ow is involved in timing as will becomeevident hereafter.

The major control element of the system is a stepping switch indicatedat 50 which comprises the conventional operating solenoid 52 effectingthrough ratchet operation the stepping of movable contacts 54, 56, 58and 60 of four banks A, B, C and D, the movable contacts engaging(functionally) fixed contacts arranged in four positions 1, 2, 3 and 4.This stepping switch may be of conventional type in which the energizingwinding 52 tensions a spring when energized, the spring then operating apawl to produce a step when the winding is de-energized. The steppingswitch is rotary so that after contact is made at 4 the next step makescontact at 1. Such stepping switches are generally provided with morethan four contacts, but may be wired in conventional fashion to producethe repeated cycling in four steps as here required. It may be herenoted that such a switch may have its wiring readily changed to producesix or some other number of steps as may be required, for example, inthe case of a triple intersection by extension of what is being heredescribed.

For convenience of reference, legends are provided at the right of theswitch indicating the trafiic light conditions existing for control ofthe NS and EW highways by its various positions, the green, yellow andred illuminated lights being indicated.

As usual, the stepping switch is provided with an interrupter involvingthe movable contact 62 engaged with the fixed contact 63 when thewinding 52 is energized, the contact being opened when the winding isenergized.

Further elements of the system are the adjustable resistors 64, 66, 68and 70 which may be independently adjusted to provide proper timing aswill be more fully described hereafter. Another pair of adjustableresistors is indicated at 72 and 74, these being settable for adjustmentof the duration of yellow lights.

The various adjustable resistors which have been described controlcurrents for the charging of a capacitor 76. Time intervals areestablished by such charging which occurs at variable rates dependingupon the settings of the resistors and which, alone or in combination,are involved in the charging. Normal leakage of the capacitor 76 throughthe emitter of a unijunction transistor 78 may take care of spuriousconditions which may occur to restore the system to normal; or, ifdesired for more rapid discharge, the capacitor 76 may be shunted by asuitable bleed resistor.

The potential buildup at the ungrounded terminal of the capacitor 76 isutilized to fire the unijunction transistor 78, the emitter of which isconnected to the ungrounded capacitor terminal. One of the bases of theunijunction transistor is connected to a positive supply terminal. Aswill appear in the further description, a number of these positivesupply terminals are indicated in the daigram. It will be understoodthat they are actually the same terminal and have been indicatedseparately only to simplify the diagram. The positive terminal of avoltage supply is connected to these terminals, the supply beingconventional and not shown since it may be provided from the alternatingpower supply line through the usual rectiler and filter system. Thenegative terminal of the supply is grounded. The control system may beoperated at a low direct voltage such as l to 25 volts with low currentsflowing through the mechanical contacts so that these are not subject tobeing damaged by burning.

The second base of the unijunction transistor is connected to groundthrough the load resistor 80 and is connected at 82 to the gate terminalof a silicon controlled rectifier 84. The cathode of this rectifier isconnected to ground while its anode is connected to the contact 63. Thecombination of the unijunction transistor and the silicon controlledrectifier provides a sufficient heavy current surge to energize thewinding 52. The unijunction transistor provides ample current to thegate terminal of the rectifier while drawing only a minute currentthrough its emitter as the capacitor 76 charges. The operation of thearrangement just described is as follows:

When the capacitor 76 becomes charged to a critical potential, theunijunction transistor 78 is fired and in turn fires the siliconcontrolled rectifier. The surge of current energizes the Winding 52tensioning the stepping switch spring and opening the contact at 62, 63.This removes the supply of current to the silicon controlled rectifierand since the capacitor 76 immediately discharges when firing of theunijunction transistor occurs, all of the parts are restored to theirquiescent state. When the winding 52 is thus de-energized, a step of theswitch occurs.

At this point manual control may be conveniently described. The positivesupply terminal is connected through resistor 86 and capacitor 88 to thejunction between resistor 90 and diode 92 polarized as indicated. Thecathode of this diode runs to the connection `82. The lower terminal ofthe resiistor 90 is grounded. 'Ihe junction between resistor 86 andcapacitor 88 is normally grounded through the manual pushbutton switch94. The last assembly has no effect on the operation previouslydescribed resulting from charging of capacitor 76. But if the switch 94is momentarily opened, a positive pulse is applied through capacitor 88and diode 92 to the gate terminal of the rectifier 84 to fire it andproduce a step of the switch as previously described. This provides formanual stepping of the switch by a traffic ofiicer if he takes overcontrol of the intersection. The stepping may be as rapid as he desires.To make manual operation entirely independent of vehicle control anormally closed switch 77 may be opened to prevent charging of capacitor76.

Interconnection of the various elements may now be described.

The normally closed contact 30 of relay 22 is connected at 96 to thefixed contact in position a of bank I of the function switch and to theupper terminal of adjustable resistor 66. The normally open contact 32of relay 22 is connected at 98 to the movable contact 44 of bank III andalso to movable contact 48 of bank V of the function switch. The movablecontact 26 of relay 22 is connected through diode 27 and connection 100to the fixed contact in position 3 of bank A of the stepping switch 50and to the xed contact in positions b and c of bank IV of the functionswitch.

The fixed contact 34 of relay 24 is connected at 102 to the fixedcontact in position a of bank II of the function switch, and at 104 tothe upper terminal of the variable resistor 70. The fixed contact 36 ofrelay 24 is connected at 106 to the movable contact 46 of bank IV of thefunction switch and to the upper terminal of the variable resistor 68.The movable contact 23 of relay 24 is connected through diode 29 andline 108 to the fixed contact in position b of bank I of the functionswitch and to the fixed contact in position I of bank A of the steppingswitch 50. It is also connected through the diode and line 110 to thefixed contact in position c of bank V of the function switch.

The movable contacts 40 and 42 are connected to the positive supplyterminal, as is also the movable contact 54 of bank A of the steppingswitch.

The lower terminals of resistors 64 and 70 are connected together at 112and to the fixed contact in position 3 of bank B of the stepping switch.

The lower terminals of resistors 66 and 68 are connected together at 114and to the fixed contact in position 1 of bank B of the stepping switch.The movable contact 56 of this bank B is connected to the ungroundedterminal of capacitor 76 through the normally closed switch 77.

The resistors 72 and 74 have their lower terminals connected to thepositive supply terminal and their upper terminals are connectedrespectively at 116 and 118 to the fixed contacts in positions 2 and 4of bank B of the stepping switch.

The last two banks C and D of the stepping -switch control the signallights 120 122, 124, 126, 128 and 130 at the intersection. The firstthree of these control the traffic on the NS highway 2, while the lastthree control that on the EW highway 4. One terminal of each of theselamps is connected to one side of the alternating current power lineindicated at 132. The individual lamps are connected through the siliconcontrolled rectifiers 134, 136, 138, 140, 142 and 144, respectively, tothe other side of the line. To the last side of the line the movablecontact 58 is connected through the diode 146 and resistor 148, whilethe movable contact 60 is similarly connected through the diode and theresistor 152. The gate terminals of the rectifiers are respectivelyconnected to the fixed contacts of the banks C and D through the lines154, 156, 158, 160, 162 and 164, respectively. As will be evident, theconnections are so arranged as to produce for the successive positionsof the stepping switch the control light indications shown at the rightof the stepping switch.

While sufficiently heavy contacts of the stepping -switch could controlthe respective lamp currents directly, it is desirable, to avoidoverloading and consequent damage and to make use of a conventionalsmall size stepping switch, to utilize the switch to control the siliconcontrolled rectifiers which are capable of handling what may be quiteheavy currents particularly at intersections where the single lampsillustrated are duplicated in parallel. At important or dangerousintersections multiple lamps are thus used. The resistors 1148 and 152limit the control currents to suitable values and the diodes 146 and 150prevent reverse current ows. In the arrangement illustrated half-cycleenergization of the lamps is provided, and the operation of therectifiers is conventional and need not be described in detail. It willbe evident that the lamp current control switching arrangement may beextended in obvious fashion to the control of more elaborateintersections and may include provisions for the showing of red signalson both intersections simultaneously to permit pedestrian crossing, orthe like. This, of course, involves corresponding control of the stepsof the stepping switch, but such extensions will be obvious, involvingwhat are, in effect, multiple step controls of the type provided for theshowing of yellow lights.

There will now be described the aspects of control of the steppingswitch in the automatic operation established by the positioning of thefunction switch 38 with its movable contacts in position c. It will benoted that this position involves the movable contacts 40 and 42 inineffective positions so they may be disregarded in what follows.

First, there may be considered what occurs when the stepping switch isin position 1 (showing green for the NS highway), assuming no traic oneither highway so that both relays 22 and 24 are de-energized.

For any stepping to occur, the capacitor 76 must be charging to reach afiring potential for the unijunction transistor 78, and the circuit maybe best considered by following it backwardly from the upper terminal ofcapacitor 76 to consider whether or not charging current flows thereto.If the circuit is thus traced for the condition described, i.e., bothrelays de-energized, it will be found that no path leads from thecapacitor to a positive supply terminal, and accordingly there is nocharging so that the condition remains fixed. The same situation will befound to be true if the stepping switch is in position 3. In otherwords, in the absence of any traffic the system remains in the conditionfinally assumed after a preceding operation under vehicular control,such stable positions being 1 and 3.

At this point it will be convenient to consider the situation which willexist if the stepping switch is in position 2. This position presents ayellow signal to the NS highway and a red signal to the EW highway. Inthis position it will be seen that tracing a circuit from the upperterminal of capacitor 76 connections run through movable contact 56 ofbank B, connection 116 and resistor 72 to the positive supply terminal.Charging therefore occurs at a rate determined by the setting ofresistor 72. The result is the ultimate production of a step of theswitch 50 to position 3. It will be noted that the connections justdescribed are completely independent of the conditions of the relays 22and 24, and hence whenever position 2 of the stepping switch is attainedthere will be initiated a step to position 3 irrespective of any otherconditions in the control system. In similar fashion when position 4 isattained there will be a step to position 1 -under control of thesetting of resistor 74. The resistors 72 and 74 accordingly determinethe duration of yellow signals. By reason of independent settability,the yellow signals for the respective highways may be caused to persistfor different times; it is usually desirable to have a long yellowsignal exhibited on a high speed highway to give ample warning of animpending transition to red so as to avoid the necessity for suddenstops, whereas shorter yellow signals may be provided on lower speedhighways to minimize delays in traic flow. It will now be evident thatwhat has just been desecribed for the timing of yellow signals may beextended to the timing of walk signals when desired, there beingprovided additional steps of a stepping switch which from the standpointof operation are controlled in the fashion just described. A yellowsignal, for example, may be followed by a red signal on both highwayswith simultaneous exhibition of a signal indicating that pedestrians maycross the intersection. In general the pedestrian signal may be of afixed duration.

Next to be considered is the condition which exists when a particularhighway has a green signal and traffic continues on this highway withoutthe appearance of a vehicle in a detection zone on the other highway.Under these conditions the green signal should continue withoutinterruption until a change is required by a vehicle on the otherhighway. The situation may be considered by assuming that the steppingswitch is in position 1 giving clearance to t'he NS highway. Under theseconditions traffic on the NS highway may continuously or intermittentlyenergize the relay 22. The condition for relay 22 de-energized hasalready been considered. If relay 22 is energized, relay 24 beingde-energized, tracing of the circuit backwardly from the capacitor 76will reveal that no path is connected to a positive supply terminal forcharging. One connection, however, may be especially noted: goingbackwardly through contact 56, connection 114, resistor 68, line 106,contact 46, and line 100, we arrive at diode 27. It will be found thatbecause of the energized condition of relay 22 a positive potential doesappear at the movable contact 26 which is closed against 32. But thediode 27 is disposed to block charging flow so that the path justdescribed is effectively open. The minute leakage current through thediode 27 will be so small as to flow off through the emitter ofunijunction transistor 78 and, accordingly, no effective charging ofcapacitor 76 takes place.

The result is that in the absence of the appearance of a Vehicle on theEW highway the green signal will be maintained for the NS highway.

`Considering the symmetry of the circuit, it will be evident thatsimilar conditions exist if the stepping switch is in position 3 andtraffic is solely on the EW highway. In this last case the diode 29performs the same blocking function as the diode 27 previouslydescribed.

The next condition which may be considered may be that assuming thestepping switch in position 1, exhibiting a green signal on the NShighway with traffic continuously within one or both of the NS detectionzones but with a vehicle entering one of the EW detection zones. Whenthis last occurs both relays are energized.

If connections are now traced backwardly from capacitor 76, it will befound that no connection to a positive supply terminal exists throughthe resistor 66. However, a connection to a positive supply terminalthrough resistor 68 does exist which may be traced as follows: fromcapacitor 76 through contact 56 to connection 114, thence throughresistor 68, to connection 106, through the closed contact at 36, 28,through diode 29, and line 108 and through Contact 54 to the positivesupply terminal. Considering these connections, the diode 29 is disposedfor forward ow of charging current. No other paths to a positive supplyterminal exist, and consequently the capacitor 76 is charging solelythrough resistor 68. Under the assumption of a heavy traffic flow onhighway NS, the resistor 68 may be assumed adjusted to provide arelatively high time constant to permit disposal of the NS traffic. But,though the delay may be relatively long, a step will ultimately occur toposition 2 and then, as described, to position 3 to stop the NS trafficand give a green light to the EW vehicle or vehicles.

The situation thus presented is highly desirable: a maximum flow oftraffic on the NS highway is permitted and, in particular, a situationis presented which will clear through the intersection a group ofvehicles which may initially have been stopped in one of the NSdetection zones, for example, 8. If a number of vehicles are stopped inthis zone, for example, by reason of the leading one having beenstopped, and perhaps making a left turn, the long delay may be set toafford time for successive vehicles to get under way and clear theintersection before movement on the EW highway starts. As is well known,if a number of vehicles are stopped, as each moves there is asubstantial time delay for the next to get under way, usually a matterof several seconds. A group of vehicles thus stopped should be permittedto clear the intersection following movement of the first.

However, once the detection zones of the NS highway are free ofvehicles, movement on the EW highway should promptly occur. This iseffected as follows:

Under this last condition the relay 22 will be de-energized while relay24 will be energized. Tracing the circuit back from the capacitor 76,there will be found to exist the connection to the positive supplyterminal through resistor 68 as before. But there will now also be foundto exist a second charging circuit through resistor -66 as follows:through contact 56 to connection 114, through resistor 66 and connection96, through the now closed contacts 30 and 26, through diode 27, throughconnection 100, through contact 4, and to line 106 and thence as beforeto the positive supply terminal. The result is that the capacitor 76 isthen being charged through both resistors `66 and y68 in parallel toprovide a more rapid charging. In fact, resistor 66 may be adjusted tohave a much lower resistance value than resistor 68. If during thischarging another vehicle passes through a detection zone of highway NS,the charging through resistor 66 may be interrupted, but whenever nosuch vehicle appears, the charging rate is speeded up. The time for thetransition to position 2 is therefore a minimum if no vehicles appear inthe detection zone in highway NS, and the delay is maximum if vehiclesare continuously in those detection zones. For intermediate conditionsthe transition is speeded up in favor of the establishment of EW trafficflow.

As will be clear from the symmetry of the circuit, similar conditionsexist in the transition from position 3 of the stepping switch with, ofcourse, reversal of the highways considered. In this last case,resistors 64 and 70 are involved rather than resistors 66 and 68. Sinceall four of these resistors are separately adjustable, maximum andminimum times may be set to suit what are normal traic conditions. If,during the course of the day, traffic iiow conditions change, an oiiicermay readily change the settings of the resistors, including resistors 72and 74, to suit new conditions. For example, it may well occur thatusually the NS highway carries heavy traffic and the EW highway may haverelatively light traic. But if a plant is located on the EW highway andat a particular hour a large number of employees are leaving the plant,preferential treatment may be `given to the EW traflic to dispose of itmost expeditiously.

The system also takes care of certain transient conditions. Note thatthe relays 22 and '24 are closed only when a vehicle is in acorresponding detection zone. Suppose that a vehicle proceeding north onthe NS highway makes a right turn at the intersection to proceed east,and swinging widely moves momentarily into the detection zone 14. Thiswould, of course, start a timing action similar to what would occur if avehicle moving west entered the same detection zone. But if it entersand then leaves the zone 14, the charging of capacitor 76 will beinterrupted at the time of leaving, and a step of the switch 50 will notoccur. The partial charge thus produced on the capacitor 76 willgradually leak away through the emitter of the transistor 78, or, aspreviously indicated, there may even be provided an actual leakageresistor across the capacitor 76. Even if no leakage occurred, the onlyresult would be to produce a somewhat shorter than normal charging timefor the capacitor after another vehicle enters the detection zone 14.'Similar transient conditions might also occur, for example, if aprivate lane existed at the position of a detection zone so that itwould be entered for a short interval by a vehicle moving into the lane.

The foregoing covers the operations involved when the function switch 38is in the automatic position c. There may now be considered theconditions which exist when the setting is in the semi-automaticposition b,

The semi-automatic position of the function switch involves operationdilfering from the foregoing only in that after position 3 of thestepping switch is achieved there will occur automatic stepping toposition 1 whether or not a vehicle appears in a detection zone of theNS highway. This means that unless a vehicle on the EW highway hasenforced a different situation, the NS highway will always have a greenlight so that traic thereon need not slow down except possibly justafter a vehicle on the EW highway has exerted control. In other words,high speed traffic liow may exist on the NS highway except under unusualconditions.

From the standpoint of operation there need only be considered thecondition in which the stepping switch is in position 3. The chargingcircuit may be traced from capacitor 76 through movable contact S6 toconnection 112 and thence through resistor i64 and contact 42, now inposition b, to the position supply terminal. A charging circuit is thusset up which is independent of conditions of the relays 22 and 24. Thereistor 64 is that which establishes a maximum time delay in favor oftraffic on the EW highway before the stepping to the fourth position.

If relay 24 is energized by one or more vehicles in the detection zoneof the EW highway, charging is solely through the resistor 64. But assoon as no vehicle is in either of the detection zones 12 or 14, relay24 is deenergized, and another charging path may be traced fromconnection 112 through resistor 70, through the closed contacts at 34and 28, through diode 29 and connection 108 and then through movablecontact 40 (in position b) to the positive supply terminal.- In thiscase charging is through both resistors 64 and 70 in parallel and aquick stepping to position 4 and then to position 1 will take place. Allof the other operations of the control are the same as described for theautomatic setting of the function switch 38 and need not be repeated.The sole difference is the automatic return of the stepping switch toposition 1 which is maintained except when a vehicle on the EW highwayrequires clearance.

Position a of the function switch 38 is referred to as a fixed timesetting though this may or may not be strictly the case depending uponthe settings of the resistors of the group 64-70. If the resistors 66and 70 are set at values much less than the resistors 64 and 68, timeswill be essentially constant irrespective of detections of vehicles andthe system will then function effectively the same as thatconventionally controlled by a time switch. However, in this settingsome preference may be given to vehicles 'which are in the detectionzone to speed up the cycling to some extent.

Considering the function switch 38 in position a, and the steppingswitch in position 1, a charging circuit may be traced from capacitor 76through contact 56, connection 114, resistor 66, connection 96, andcontact 40, in position a, to the positive supply terminal, Charging isthus effected through the resistor 66 independently of the conditions ofthe relays 22 and 24. However, if relay 24 is energized, anotherparallel circuit may be traced from connection 114 through resistor 68and connection 106 through the closed contacts 36 and 28, through diode29 and then through connection 108 and contact 54 to the positive supplyterminal. If resistor 68 is set at a value comparable with or less thanresistor 66, the presence of a vehicle in a detection zone of the EWhighway will ac- 1 l celerate the stepping to position 2 and thenceautomatically to position 3.

If the switch is in position 3 a similar situation exists, chargingybeing through contact 56 and connection 112 and thence through resistor70, connections 104 and 102, and through contact 42 to the positivesupply terminal. This charging path is independent of the conditions ofthe relays. If relay 22 is energized, there is a further charging paththrough resistor 64, contact 44, connection 98, closed contacts 32 and26, diode 27, connection 100 and contact 54 to the positive supplyterminal, so that charging then is through both resistors 64 and 70 inparallel to speed up the transition to position 4 and then toposition 1. This so-called xed time adjustment may be used 'when thereis traffic congestion on both highways. It will be evident that byadjustments of the resistors, however, the time for transition fromposition 1 to position 3 may be made quite different from that fromposition 3 to position 1.

Manual control by the momentary openings of Switch 94 (switch 77 beingopened) can be used to override the automatic operations.

`Referring now to FIG. 2 which involves electronic control withoutmechanically moving parts except for the relays 22 and 24 and the use ofthe function-selecting switch 38 and the switches involved in manualoperation, consideration of the construction and operation will beclaried by pointing out that the relay connections to and through thefunction switch and the variable resistor arrangement are all similar towhat has already been described. The differences are basically that forthe stepping switch there is substituted a ltwo-stage counter Iwhichestablishes four conditions corresponding to the four positions of thestepping switch. Output lines from the counter control the charging of acapacitor which, in FIG. 2, provides pulses for the stepping of thecounter. The output lines from the counter also have matrix connectionsto devices including silicon controlled rectiers for control ofillumination of the signal lights.

The various parts and connections which are the same as those in FIG. lare designated by the same numerals to eliminate the necessity forrepetition of the description.

' The new and diferent connections are the following:

A line 166 connects the fixed contact at position c of an additionalbank VI of the function switch 38 to the emitter of a transistor 168,the collector of which is connected to the positive supply terminal. Insimilar fashion the connection 110 previously described is extended tothe emitter of a second transistor 170 to the collector of fwhich isconnected to the positive supply terminal. These transistors arerendered conductive as will be hereafter described to provide currentthrough the connections 166 and 110.

A set of diodes 176, 178, 180 and 182 are provided to supply independentcharging currents from the several resistors to a commoncondenser-charging line 222. The upper terminal of resistor 74 isconnected to the positive supply terminal and its lower terminal isconnected at 184 to the anode of diode 176 while the upper terminal ofresistor 72 is also connected to the positive supply terminal and itslower terminal is connected at 186 to the anode of diode 178. Theconnections 184 and 186 also run to the collectors of the respectivetransistors 188 and 190, the emitters of which are grounded.

The lines 114 and 112 are connected respectively to the anodes of thediodes 180 and 182 and to the collectors of transistors 192 and 194, theemitters of which are grounded.

A pair of resistors 200 and 202 have their upper terminals connected tothe positive supply terminal and have their lower terminals respectivelyconnected at 204 and 206 to the bases of the transistors 168 and 170.These terminals are also respectively connected to the collectors oftransistors 196 and 198, the emitters of which are grounded.

In the case of each of the transistors 188, 190, 192, 194, 196 and 198,the Vbases are individually connected to a negative potential terminal,i.e., negative with respect to ground, through resistors typied at 208.(The positive terminals heretofore and hereafter referred to are alsowith respect to ground, a three terminal direct power supply being hereused.)

The bases of the transistors just mentioned are also connected throughrespective resistors 210, 212, 214, 216, 218 and 220 to paired diodesdescribed later.

The capacitor charge through the connection 222 is indicated at 224, andat this point there may be described the type of operation involved inthe selective charging of this capacitor through the resistors 64, 66,68, 70, 72 and 74. lf the transistors 188, 190, 192 and 194 areconducting, the lower terminals of the resistors are effectivelygrounded and consequently no positive outputs are provided from theirconnections 184, 186, 114 and 112. But if any one of these transistorsis cut olf by reason of a negative base, the ground connection ifeffectively open so that a positive potential is applied to the anode ofthe corresponding diode of the group 176, 178, 180 and 182 to provide acharging current. As will appear, the control system renders selectivelynon-conductive these transistors which are normally conductive. Thediodes block reverse current ows.

Somewhat similar considerations apply to the controls of the transistors168 and 170. When the diodes 196 and 198 are conducting, the bases ofthe transistors 168 and are grounded and the transistors do not passcurrent from the positive terminal. However, when the transistors 196and 198 are selectively cut off by negative potentials applied to theirbases, the bases of the transistors 168 and 170 become positive throughthe connections of resistors 200 and 202 to the positive supplyterminal, and the transistors 168 and 170l accordingly supply currentthrough their emitters.

The ungrounded terminal of capacitor 224 is connected to the emitter ofthe unijunction transistor 226, the upper base of which is connected tothe positive supply terminal while the lower base is connected throughthe load resistor 228 to ground. The lower base of the unijunctiontransistor is connected through capacitor 230 and the normally closedswitch 234 to the base of the transistor 236 which is connected throughresistor 232 to ground. Por manual operation the switch 234 is engagedwith the upper contact 237 to the junction of resistor 238 and capacitor240. The upper terminal of resistor 238 is connected to the positivesupply terminal, while the lower terminal of capacitor 240 is grounded.A normally closed pushbutton switch 242 grounds the junction 237. Formanual operation, with the switch 234 in its upper position, the pushbutton switch 242 is opened, and its opening produces a positive pulsethrough resistor 238 to the base of transistor 236. In other operations,the firing of the unijunction transistor produces positive pulsesthrough the capacitor 230 and the normally closed lower position of theswitch 234 to the base of transistor 236.

The emitter of transistor 236 is grounded and its collector is connectedthrough load resistor 244 to the positive supply terminal. It is alsoconnected through diode 248 to the lower terminal of resistor 246 whichruns to the positive supply terminal. The anode of the diode 248 isconnected to the line 250. When the transistor 236 is non-conducting,the line 250 is positive; but when the transistor 236 conducts, the line250 is effectively grounded, and when this conduction occurs a negativepulse is delivered through the line 250.

Control is eifected through the counter comprising the bistablemultivibrators V252 and 254 which are conventional and need not bedescribed in detail. Counting is effected by the delivery of thenegative pulses through line 250` to the rst multivibrator and throughdelivery of negative pulses to the second multivibrator through thediode 264 from the output of the first multivibrator appearing on linel258. Two-stage binary counting is thus effected. Pour output lines 256,258, 260 and 262 run from the multivibrator stages as shown andselective connections to these effect the control operations. As usual,four configurations exist, lines 256 and 258 always being of oppositepolarity and lines 260- and 262 also being of opposite polarity.Capacitors shown in a group at 266 are connected between these'respective lines to ground to suppress transients and noise.

The various resistors of the group 210 to 220 are selectively connectedto the lines 256, 258, 260 and 262 through diode pairs, the pair for theconnection of resistor 210 being indicated at 268. The resistor 210 isconnected to the cathodes of the diodes and the lines are selectivelyconnected to the anodes. In the case of the pair 268 the connections areto the lines 256 and 262. In the case of the diode pair 270 connected toresistor 212, the connections are to the lines 256 and 260. The diodesof the pair 272 connected to resistor 214 are connected to the lines 258and 260. The diodes of the pair 274 connected to the resistor 216 areconnected to the lines 258 and 262. The diodes of the pair 276 connectedto resistor 218 are connected to the lines 258 and 262, theseconnections being the same as for the diodes at 274. The diodes of thepair 278 connected to resistor 220' are connected to the lines 258 and260 corresponding to the connection of the diodes of the pair 272.

The connections just described control the corresponding transistors asfollows:

If either diode of a pair at any time is connected to a positive linecurrent flows therethrough and through the associated resistor and theresistor corresponding to 208 rendering the transistor base positive sothat the transistor conducts preventing charging current from flowingfrom the line connected to its collector. On the other hand, if bothdiodes of a pair are connected to negative lines, the fiow of currentthrough the corresponding resistor of the group 210, etc., is cut offand the base of the corresponding transistor is negative, cutting oicurrent fiow through the transistor so that charging of the capacitor224 from the line connected to its collector occurs. Proper switchingaccordingly results.

Control of the signal lamps is effected through units containing siliconcontrolled rectiiiers which are delimited by dotted lines in thefigure.`A resistor 280 connected to line 262 provides a control signalfor the unit 282 which will be later described in detail. Similarly aresistor 284 is connected to line '260 provides for control of the unit286.

In the case of the next four units 290, 300, 306 and 312 the connectionsare somewhat different. In the case of the third unit 290, a resistor288 is connected to the anodes of a pair of diodes 292 and 294, thecathodes of which are respectively connected to the lines 258 and 262.The anodes are also connected through resistor 296 to the positivesupply terminal.

The next unit 300 is similarly associated with a resistor 298 connectedto a diode-resistor unit 302 in which the diodes are connected to thelines 256 and 262.

Unit 306 is similarly connected through resistor 304 to thediode-resistor assembly 308, the diodes of which are connected to thelines 258 and 260. The unit 312 is connected to the resistor 310 whichis in turn connected to the diode-resistor assembly 314, the diodes ofwhich are connected to the lines 256 and 260.

The units 282, 286, 290, 300, 306 and 312 respectively supply current tothe lamps 31-6, 318, 320, 322, 324 and 326.

Instead of individual lights multiple light rnay be connected inparallel for traffic control. The light 316 is red for the EW highwaywhile light 318 is red for the NS highway. Light 320 is yellow fo rtheNS highway and light 322 is green for the NS highway. Light 324 isyellow for the EW highway and light 326 is green for the EW highway.

Referring to the components in the unit 282, resistor 280 "runs to thebase of transistor 328, this base being also connected through resistor329 to the negative supply terminal. The positive supply terminal isconnected through resistor 330 and the direct terminal winding 332 of asaturable reactor to the collector of the transistor 328, the emitter ofwhich is grounded. A diode 334 is connected between the positive supplyterminal and the collector of this transistor to take care of inductivesurges.

The alternating current winding 336 of the saturable reactor has oneterminal connected through resistor 338 and diode 340, polarized asindicated, to the anode of a silicon controlled rectifier 342, the gateterimnal of which is connected to 344 to the other terimnal of thewinding 336. One side of the alternating current supply line indicatedat 346 is connected to the anode of the rectier 342. The second side ofthis line indicated at 348 is connected thorugh resistor 352 to thecathode of the rectifier. A resistor 353 is connected between thecathode of the rectifier and its gate terminal. The light or lights 316are connected between the side 348 of the alternating current supplyline and the cathode of the rectifier. The capacitor 350 is connectedbetween the cathode of the rectifier and the right-hand terminal of thewinding 336. When the transistor 328 is non-conducting, no appreciablecurrent fiows through the control winding 332 of the saturable reactor,and accordingly the winding 336 provides a high impedance which inassociation with resistor 353 results in an insufiicient positive supplyto the gate terimnal of the silicon-controlled rectifier to fire it, andconsequently the rectifier does not supply current to the light 316. Onthe other hand, when the transistor 328 conducts, direct current iiowsthrough the winding 332 and the winding 336 presents a low impedanceresulting in a sufficiently positive supply to the gate of the rectifierto fire it during forward half cycles and thereby illuminate the light316. The circuitry just described for the illumination of the light 316is conventional and may, of course, be replaced by many other types ofcontrols. More elaborate controls may be used to provide full waveexcitation of the light.

As will now be evident, lighting vof the light corresponds to aconductive condition of the transistor 328. So long as the line 262 isrelatively negative, i.e., effectively grounded, the negative supplythrough resistor 329 maintains the base of transistor 328 negative andthe transistor non-conducting. However, if the line 262 is positive,potential at the base of the transistor is positive and conductionoccurs resulting in illumination of the light 316 as stated. Theresistors 280 and 329 are chosen to provide the proper voltage divisionfor this purpose.

The unit 286 is identical with the unit 282 and the operation is thesame, the light 318 being illuminated when the line 260 is positive.

In the case of the next four units 290, 300, 306 and 312 operation issomewhat different, depending on conditions of the pairs of lines towhich the associated diodes are connected. For example, considering theunit 290, if either of the lines 258 or 262 is relatively negative, thelower end of the resistor 296 is effectively grounded so that the baseof the corresponding transistor is held negative by the connection tothe negative supply terminal through the resistor corresponding to 329.On the other hand, if both lines 25S and 262 are positive, ow of currentthrough them is blocked, and the positive supply through resistor 296provides a positive potential to the transistor base through the voltagedivider system, and light 320 is accordingly illuminated. Similarconditions, but related to the corresponding pairs of lines, exist inthe control of the units 300, 306 and 312.

It will now be seen that switching operations are effected for bothcharging the capacitor 224 and for illuminating the lamps, the switchingbeing effected in accordance with the four possible conditions of thebinary counter, the conditions of which are stepped in sequence by thefiring of the unijunction transistor 226 upon adequate charging of thecapacitor 224. The matrix system provided by the lines 256, 258, 260 and262 and the connections described controlling the step operations. Theswitching may be readily followed by considering the following:

When the lines 256, 258, 260 and 262 are respectively positive,negative, negative and positive the green light 322 for the NS highwayis illuminated and simultaneously the red light 316 for the EW highway.The next step results in the respective conditions of the linesnegative, positive, negative and positive, and the yellow light 320 isilluminated for the NS highway While the light 316 continues red for theEW highway.

The next step results in positive, negative, positive and negativeconditions for the respective lines producing illumination of the redlight 318 for the NS highway and the green light 326 for the EW highway.The fourth step results in negative, positive, positive and negativeconditions for the respective lines, the red light 318 being continuedilluminated for the NS highway while the yellow light 324 is illuminatedfor the EW highway. The sequence is thus the same as that involved inthe case of the modification illustrated in FIG. l. The switchingsequence is identical with what has been described in detail for FIG. 1with respect to the charging operations involved through the resistors72 and 74, during a showing of yellow lights, and through the resistors64, 66, 68 and 70 and their connections 112 and 114 for the greenlights, with association of the proper red lights. Positive supplies arecontrolled through the transistors 168 and 170, and in view of the sameswitching cycle and taking into consideration the mere fact thatswitching is accomplished differently, it will be lunnecessary to tracethe charging paths which through the relay contacts and through thefunction switch contacts and resistors are the same as previouslydescribed. In view of the correspondence be tween the function switchsteps of the two modifications it will be evident that the automatic,semi-automatic and fixed time operations are the same as previouslydescribed.

It will be evident that various modifications may be made involving eventhe substitution for the relays 22 and 24 of solid state switchingarrangements. Further, it will be evident that by extensions of what hasbeen described for FIG. 2 the system is adaptable to the traffic controlof more elaborate intersections.

Having described the system specifically as it functions in variousmodes, it may be helpful to now review in more general terms thefundamental principles underlying the invention. In a digital-typetraffic control system of the type heretofore known, vehicles arecounted one by one to determine the various traffic parameters (i.e.,volume, density and speed). But these parameters do not reflect theactual tratiic conditions as they exist in the region of theintersection. In contradistinction, in the present invention theseconditions are translated into an analog value which acts to effect aphase split in the operation of the signal controller at a time bestcalculated to promote efcient traic tlow. Hence the present system,which is grounded on analog principles, is basically at variance withprior digital systems.

To explain the analog concept in general terms and without regard to anyone mode of operation, FIG. 3 shows a detector D in the left lane of aroad X which intersects with a road Y. Placed at the intersection is atraic signal controller TSC which shall, for reasons of simplicity, beof the type having only red and green signals. The controller is capableof functioning in a phase A giving a right of way only to traic in roadX and in a reverse phase B in which this right of way is given only totraffic in road Y. The combination of the two phases constitutes theoperating cycle of the controller and the transfer point therein isdesignated the split. The transfer from one phase to another is effectedby a split switch SS which in turn is actuated by a timer T. The timer,when initiated, runs from a start point to a finish point 16 in aninterval whose duration is an analog of the trai-lic pattern in thelane, the split switch being fired when the finish point is reached.

Detector D encompasses an elongated zone in the left lane in road X, thelength of the zone being sufficient to include a plurality of vehicles,the end of the Zone being adjacent the intersection. As long as anyvehicle or a portion thereof lies Within the boundaries of the Zone,detector D will produce a 1st value which represents a state ofoccupancy, but when no vehicle or any portion thereof lies withinthevzone boundaries, a 2nd value is established representing a state ofnon-occupancy. If therefore a platoon of vehicles is travelling throughthe detected zone and one or more vehicles thereof lies fully orpartially within its boundaries, detector D yields the 1st value, butwhen the headway between two vehicles in the travelling platoon is suchthat at a particular time no one vehicle falls within the zoneboundaries, the detector yields the 2nd value. While a high-frequencyloop detector has been disclosed for this purpose, it will be obviousthat other known forms of presence detectors may be used within thescope of the invention.

Detector D is operatively coupled to timer T. The operation of the timeris expressed in terms of a voltage which rises along a ramp from a zeroor minimum level at the start point to a predetermined voltage magnitudeor maximum level at the nish point. As shown by the various curves inFIG. 4, the amount of time, in seconds, it takes this voltage to risefrom the start to the iinish point represents the timing interval whichconstitutes the analog value. While the timer is described as electronicin character, it will be obvious that equivalent results are obtainableby a mechanical or motor-driven arrangement.

Timer T is arranged so that when it is responsive to the lst value itruns slowly, this being represented by the maximum setting voltage curveI, where it will be seen that it takes 30 full seconds for the voltageto rise from start to finish. When however the timer responds to the 2ndvalue, it runs much faster. This is represented by the minimum settingcurve II, where it will be seen that the voltage runs from start tofinish in exactly 3 seconds, which is ten times as fast as the responseto the 1st value.

If therefore there is no traffic in the zone at the time the operationof the timer is initiated and this condition continues, the timer 'willtime out quickly, as in curve 1I, to cause a split after the threesecond minimum interval. But if the traiiic is such that the zoneremains occupied by one or more cars, the timer will time out slowly, asin curve I, to cause a split only after a thirty second interval, thusaliording the maximum time to clear traic through the intersectionbefore the split occurs.

If on the other hand, the traffic pattern is fluctuating so that thezone is intermittently occupied, the detector Will yield 1st and 2ndValues in a sequence reflecting this condition. Consequently, as shownin curve III, the voltage will rise quickly when a 2nd value is inforce, then slow down when a 1st value takes effect, so that the timinginterval between start and finish will be made up of successive slow andfast increments (A, X, B, Y, C and Z).

The total interval (Curve III-17 seconds) will therefore be an analog ofactual traic conditions, and will reflect the physical length of thevehicles as well as speed, starting time, headway and other parameterswhich come into play and to which the detector is sensitive.

In order to further explain why the timer interval constitutes an analogof tratiic conditions, some examples will now be given. Assume that asingle car is passing through the detected zone at I20 miles an hour. Aslong as this calor a portion thereof lies within the zone boundaries, a1st value will be produced which reects the state of occupancy. As soonas this car is fully outside of the zone boundary, the 2nd value isestablished. In a simple practical form, these values may be created bya relay which is caused to occupy one switch position when the detectoriield intercepts the presence of a vehicle and another switch positionwhen no vehicle is present. In one switch position a timing circuithaving a long time constant is introduced in Timer T, while in the otherswitch position a timing circuit with a short time constant isintroduced therein.

If now a second car travels through the zone at exactly the same speed,but the second car is longer than the first, though it will take exactlythe same time for the second car to go from the beginning to the end ofthe zone, it will necessarily take longer for the second car body toclear the end of the zone. This will be refiected in the relativeperiods of the lst and 2nd values produced by the travel of the secondcar. Hence while a digital system will not be able to distinguishbetween the first and second cars in the example given, in that each cargives a single count and each produces the same speed indication, theanalog system will afford an appropriate distinction, for the resultanttiming interval will reflect the longer occupancy period of the secondcar and therefore have a greater duration.

Let us now by Way of another example assume a platoon of cars travelingthrough the zone, all cars having the same speed and being spaced apartwith a headway say of 100 feet. The resultant 1st and 2nd values will ofcourse reflect this headway in the relative periods in which the twovalues are established. If now another platoon of cars travels throughthe zone and the cars in this platoon are identical to those in thefirst and are moving at the same speed, but with a headway of 200 feet,this distinction will show up in the values established by the detectorand by the resultant timing in period. Thus regardless of how trafficfluctuates, the analog system will produce an analog voltage which is aproper refiection of the existing conditions, and the instant of phasesplit in the signal controller will be such as to produce right of waysignals promoting optimum fiow efficiency.

Thus if the detector loop is immediately vacated, the timer will timeout on its minimum setting, if the loop is continuously occupied, thetimer will time out on its maximum setting, and if the loop experiencesa combination of occupancy and non-occupancy states, it will time out atsome intermediate point between the minimum and maximum time setting.This analog principle lends itself to various modes of traffic controloperation.

Thus in the semi-actuated mode, with an intersection of a major andminor artery, minimum green time can be guaranteed on the major arteryby means of a detection loop on the minor artery providing a right ofway only on demand. That is, the arrival of a car in the minor arterydetection zone causes the phase to split and gives the minor artery agreen for an interval which is then subject to analog control. This isaccomplished by a gate circuit which normally disables the timer andinitiates its operation only on the arrival of a vehicle in the minorartery.

In a fully-actauted with preference mode, there is full detection inboth phases, but the green time reverts to the parent phase (mainartery) if there is no demand on the minor artery. Each artery is timedon the analog principle. In fully actuated without preference mode therevert feature is omitted, the operation otherwise being the same. Inthe fully-actuated, last call mode there is again full detection on bothphases, but green remains on phase until detection on opposite phase,each artery being timed on the analog principle. In the fully-actuatedtwo phase recall mode, in the absence of traffic, right of way transfersback and forth on minimum time setting. However, the arrival of trafficwill allow green up to the maximum setting of either phase on the analogprinciple.

It will be appreciated that regardless of the mode, an analog system isused which combines a true presence detector with a timer to produce ananalog interval at the end of which a split phase occurs. Differences inmodes depend on the manner in which the operation of the timer isinitiated and whether timing takes place in the major as well as theminor artery. Analog systems may be installed at a progression ofintersections, the systems being coordinated so that the operation ofany one intersection is under the control of the system at a precedingintersection.

While there has been shown and described a preferred embodiment of ananalog trafiic control system in accordance with the invention, it willbe appreciated that many changes and modifications may be made thereinwithout, however, depending from the essential spirit of the invention.

What I claim is:

1. An analog system for controlling vehicular traffic at an intersectionof two roads, said system comprising:

(a) a traffic signal controller disposed at said intersection andoperable in one phase to give a right of way only to traffic in one roadand in a reverse phase to give a right of way only to traffic in theother road,

(b) a split switch coupled to said controller to cause the phase thereofto transfer from the existing phase to the other phase,

(c) a detector disposed in one of said roads to sense either thepresence of any vehicle or a portion thereof in a zone having a lengthsufficient to include a plurality of successively arriving vehicles, orthe absence of all vehicles from said zone, said zone terminating at apoint adjacent said intersection, said detector yielding a first valuerepresenting a state in which the zone is occupied by at least onevehicle or a portion thereof and reflecting the headway between vehiclessuccessively arriving at the zone where said headway is no greater thanthe length of said zone, and a second value representing a state inwhich the zone is totally unoccupied,

(d) a timer coupled to said detector and responsive to said values, saidtimer running from a start point to a finish point at a rate which isslow when said first value is in force and which is fast when secondvalue is in force to produce a timing interval which is an analog oftraffic flowing through said zone, and

(e) means coupled to said timer to actuate said split switch when saidinterval reaches said finish point to cause a transfer in the phase ofsaid controller and thereby to deny a right of way to the trafficpassing through said zone.

2. A system as set forth in claim 1 wherein each lane in theintersecting roads has a detector installed therein, each detectorcooperating with said timer-to provide analog control for that lane.

3. A system as set forth in claim 2 arranged to provide operation in thesemi-actuated mode.

4. A system as set forth in claim 3 arranged to provide operation in thefully actuated mode.

5. Apparatus for control of vehicular traffic at an intersection of tworoadways including signal means controlling trafiic on said roadways byalternatively permitting or denying access therefrom to theintersection; a presence detector means associated with each of saidroad-ways responsive to the presence of any vehicle in a zone of itscorresponding roadway extending from a first point adjacent to saidintersection to a second point a substantial distance in advance of theintersection such that there may be simultaneously in said zone aplurality of vehicles one following another; a pair of switching means,one of which is operated by each detector, each switching means havingtwo states, an absence state which is established by its detector aslong as no vehicle is present in the corresponding zone and a presencestate ywhich is established as long as any vehicle is present in thecorresponding zone; an interval timing means having means forcontrolling its timing rate between an instant of initiation of itsoperation and attainment of a predetermined state of terminaion of itsoperation; cyclical switching means having sequential states within acomplete cycle of operation and effective in each state to provide apredetermined condition of said signal means; circuit means forinitiation of operation of said timing means controlled by one of saidswitching means in a presence state established by its detector when avehicle is in its corresponding zone and denied access to theintersection; said circuit means also controlling operation of saidtiming means at one rate -when both of said switching means are inpresence states, and for controlling operation of said timing means at adilerent faster rate when that switching means other than the one whichinitiated the operation of the timing means passes into its absencestate; and means controlled by said timing means when it attains saidpredetermined state to advance said cyclical switching means to the neXtState of the cycle.

6. Apparatus according to claim 5 in which said interval timing meanscomprises a resistance-capacitance timing circuit having a variable timeconstant, and said circuit means for initiation of operation of saidtiming means 20 determined state of said timing means being apredetermined charge of said capacitance.

7. Apparatus according to claim 5 in which said resistance-capacitancetiming circuit comprises means providing alternative resistances toestablish different time constants of said assembly.

References Cited UNITED STATES PATENTS 3,258,744- 6/1966 Auer 340373,258,745 `6/1966 Auer 340-37 THOMAS B. HABECKER, Primary Examiner U.S.C1. X.R.

provides current ow in said timing circuit, the said pre- 15 340-38

